1. Field of the Invention
The present invention relates to a roller conveyor allowing a program to be changed depending on a change in conveying requirements imposed along a path of conveyance and allowing radial bearings to be reliably protected against an axial external force.
2. Description of the Prior Art
In the roller conveyor of prior art comprising a plurality of rollers arranged in parallel to one another so that an object to be conveyed is placed thereon and conveyed, the rollers of three types are selectively employed at the locations suitable for them along the path of conveyance depending the conveying requirements in order to achieve the desired conveyance free from a slippage between the object to be conveyed and the rollers. More specifically, at the location where the object should be forcibly moved, said object is moved by the drive roller adapted to rotate integrally with the sprocket which is in engagement with the drive chain. At the location where the object should be moved by means other than the drive roller, the free roller rotatably supported is used so that free movement of the object can be assured. At the location where movement of the object should be temporarily inhibited by making said object bump against the stopper, the friction roller adapted to rotate integrally with the sprocket under effect of a frictional force is used so that, when movement of the object is inhibited by the stopper, the friction roller ceases to rotate against the frictional force between the friction roller and the sprocket continuing to rotate and, once the inhibition by the stopper is lifted, the friction roller rotates integrally with the sprocket to move the object.
However, the conventional roller conveyor is of the arrangement such that the drive roller, the free roller and the friction roller can not be utilized for purposes other than their respective exclusive purposes as mentioned above and, consequently, it has conventionally been impossible to replace these rollers by those of different types. Accordingly, for particular conveying requirements imposed along the path of conveyance, e.g., locations at which the object to be conveyed should be moved or stopped and a particular sequence of operating steps, it has inconveniently been necessary to prepare a specific roller conveyor which is useful exclusively for such particular requirements, namely, which is particularly arranged so that the respective rollers are arranged at the locations suitable for them.
In the roller conveyor of prior art, the friction roller has usually been constructed as will be described. Specifically, the friction roller comprises a hollow roller supported by radial ball bearing around a center shaft so that said hollow roller is rotatable around the axis and slightly movable along the axis and a sprocket supported by said center shaft so that said sprocket may be rotationally driven by engagement with a chain but axially unmovable. An axial force of a compression coil spring mounted on the hollow roller adjacent one end thereof biases the hollow roller in a direction such that a friction surface defined by the hollow roller at the other end is biased against a friction surface difined by the sprocket. A frictional force generated by this contact between the friction surfaces causes the hollow roller to be rotated in operative association with the sprocket. When the object to be conveyed is inhibited from further movement, a slippage occurs between the friction surfaces and stops rotation of the hollow roller.
In the friction roller of such construction, said compression coil spring has its opposite ends bearing against a spring shoe mounted on the center shaft, on one side, and against an inner race of the radial ball bearing, on the other side, so that the axial biasing force of the compression coil spring which is directly exerted on the inner race is then transmitted through balls and an outer race of the radial ball bearing to the hollow roller. Consequently, the radial ball bearing is often exposed to an unbearably large axial force between the inner race and the balls as well as between the balls and the outer race, resulting in a defective function and a shortened life of the radial ball bearing.